This invention relates to the polymerization of olefins by the coordinate complex method, often termed the Ziegler-Natta method after the names of the two workers who contributed so much to its practical development and theoretical basis. More particularly, this invention relates to novel, activated supports for the transition metal catalytic component.
About 30 years ago the original Ziegler-Natta catalysts were heterogeneous slurries formed in place when solutions of organometallic cocatalysts, preferably taken from the compounds of metals of Groups IA, IIA, and IIIA of the periodic table, were added to solutions of transitional metal catalysts, preferably taken from compounds of metals of Groups IIIB, IVB, and VB of the periodic table. These catalytic systems by today's standards did not have high activity in terms of grams polyolefins produced per gram catalyst component. Nor, when propylene or other monomers capable of giving polymers with tacticity were employed, did these early catalytic systems provide polymer with high isotactic index. Also, the particle size distribution of the polyolefin was too broad, leading to an undesirable fraction of "fines", particles less than about 100-180 .mu.m.
More recently, high activity, high isotactic index, and enhanced particle size have been achieved by employing catalyst supports on which catalytic transition metals have been dispersed. It has been theorized that the concentration of active polymerization centers is as much as 50 percent higher on supported catalysts than unsupported catalyst systems. These developments are discussed in the Kirk-Othmer "Encyclopedia of Chemical Technology", third edition, vol. 16, pp. 453-469 in an article entitled Olefin Polymers (Polypropylene) and in Angewandte Makromolekulare Chemie, 94, 63-89 (1981). One support which has gained favor in technical circles is magnesium halide, particularly in an activated condition. The preferred method for activating catalyst support such as magnesium halide is dry milling, as disclosed in British Pat. No. 1,335,887.
Dry milling suffers from many practical defects. Among these are long milling regimes, losses of support by "hold-up" in the milling equipment, excessive handling, the cost of milling energy, and a wide dispersion of the particle size of the milled products leading to excessively broad particle size distribution of the polyolefin. It would be advantageous to have the high catalytic activity of a supported catalyst, the high isotacticity of polymers capable of such (e.g., polypropylene) and a decreased proportion of "fines" without the necessity of a milling or grinding step. This is achieved by use of the present invention.
U.S. Pat. No. 4,071,674 discloses a transition metal catalyst component prepared by reacting a titanium or vanadium compound with the reaction product formed between an alcohol-adduct of a magnesium dihalide solid carrier and an organometallic compound of a metal of Groups I to III. No additional electron donors are employed in the process of that disclosure, and pulverization by means of a ball mill may be used.
In U.S. Pat. No. 4,076,924 a process is disclosed for preparing a solid titanium catalyst by first reacting a magnesium dihalide, an organic ester, an organic compound containing an active hydrogen atom, and an organometallic compound. Then the solid is treated with a titanium compound in the absence of the organometallic compound of a metal of Groups I to III of the periodic table.
U.S. Pat. No. 4,097,409 discloses a process for producing a supported Ziegler catalyst by treating a support, obtained by heating a magnesium halide or alkoxide with silica, with a titanium compound containing halogen.
In U.S. Pat. No. 4,226,741 at Example 15 magnesium chloride suspended in an inert hydrocarbon is treated with ethanol, then caused to react with a phenol plus ethyl benzoate, plus diethyaluminum chloride. After separation it is treated with titanium tetrachloride, filtered, washed, and dried to produce a component for the polymerization of propylene.